Global variability in the platinum-group element contents of komatiites.

We report a large volume of high-precision platinum-group element (PGE) data generated from Archaean and some Early Proterozoic komatiites and komatiitic basalts spanning a wide range of ages (from ca. 3.5 Ga to ca. 2.0 Ga), petrological affinities (Munro-type, Barberton-type and Karasjok-type) and locations (i.e. Pilbara, Yilgarn, Superior, Kaapvaal and Fennoscandian Cratons). The main purposes of this study are to establish baselines for PGE contents of komatiites and, by inference, to investigate the variability in PGE contents of komatiite source regions in space and time. On the basis of the analysis of our high-precision PGE dataset integrated with the entire existing body of published high-quality analytical data on komatiites and komatiitic basalts world-wide, we conclude that PGE baseline concentrations in komatiites of different petrological affinity, lithofacies type and emplacement style are generally similar worldwide. All komatiites have relative PGE patterns showing a slight enrichment of PPGEs over IPGEs attributable to limited retention of IPGEs in mantle sources, coupled with saturation in Ir-(Os) alloys. However, significant differences and trends exist, in particular a systematic linear increase in PGE contents of komatiites with age from the oldest at >3.5 Ga to the late Archaean group at 2.7 Ga.